Pinch valves of a type which use the principle of squeezing or pinching an elastomer tube or valve sleeve to control flow of material therethrough, in a pipeline or conduit, are available in numerous types and configurations to suit a wide range of applications. They are available in manual, and/or automated forms using pneumatic, hydraulic or electric operators. The valves are available in full round configurations, or in a form of pre-pinched valves. The former, in the open position, have the same inside diameter and capacity as a pipeline in which attached. They offer a straight unobstructed flow path with maximum capacity and minimum pressure drop. Such configurations or constructions are required in some applications where working conditions such as velocity, particle size, or cleaning of the line are determining factors.
Pre-pinched valves which have an initial compression or pinching of the valve sleeve, of for example fifty percent in one direction, serve to reduce a valve closing apparatus stroke requirement by approximately the same amount, i.e. fifty percent. In this type of valve, due to the elastic nature of the valve sleeve, an elliptical port is formed which functionally has approximately ninety-five percent of the capacity of a full round valve.
Overall valve constructions can include open construction valves having an external closing or pinching mechanism mounted around the valve sleeve, or totally enclosed valves which provide support and protection for both the valve sleeve and mechanism. Each of these types of valves are suitable for use under particular circumstances of use.
Pinch valves normally display excellent flow control characteristics, primarily due to the streamlined interior of the valves which produces a minimum change in the flow path at the throttling position, and a subsequent lack of turbulence. Each overall type of pinch valve construction and form, i.e. full open or pre-pinched, serve in different areas of use with respective optimum advantages.
Generally speaking, the elastomer tube or valve sleeve is the primary element of importance in a pinch valve. It consists of an elastomer inner layer surrounded by multiple plies of fabric reinforcement. Arrangement of the fabric plies can be altered, if necessary, to suit specific application requirements. Many different elastomers are available, as are fabrics of different materials and specific constructions.
Pinch valve sleeves are normally fully compression molded to maintain construction uniformity and consistency in performance. This full compression molding integrates the fabric reinforcing plies within the elastomer material to integrate the entire overall structure.
It has been found in practice however that pinch valves made or constructed from elastomeric valve bodies as above described, frequently have a common problem in different use environments. This problem is failure of the elastomeric valve body to be restored to a fully open condition after being closed for an extended length of time. A "set" will take place in the valve body material or valve body, subsequent to a relatively lengthy closure of the sleeve by being deformed or placed in a partially or fully closed position. Under low pressure flow conditions of material passing through the valve, as compared to high pressure flow, the fluid pressure in the valve will not serve to fully open the valve body. Under some circumstances a negative pressure exists, and this increases the problems of restoration to a fully open condition.
Different attempts have been made previously to develop positive opening body sleeve conditions. Some structures have employed metal lugs in the valve body attached to a valve actuating element. In use however, such inflexible lugs tend to tear out of the relatively soft elastomeric valve body.
Another previous construction attempting to develop a positive opening body has used integrally molded flexible tabs attached to the valve actuating elements, and which serve to, at least in part, permit a positive opening of the valve body. Such a known construction is disclosed in prior U.S. Pat. No. 3,268,201, issued Aug. 23, 1966. While the construction of this patent constituted an advance in the art, there are drawbacks inherent in the structure. The tabs of this prior patent are integrally molded into the valve body, with the tab assembly including a flat tab element, the ends of which are upwardly lifted to form the tabs. This tab element is superposed axially onn the body over a so-called "belly band" which is disposed perpendicularly to the tab element. The belly band extends circumferentially partially around the valve body. The belly band constitutes an activating strap portion for applying an opening force to the sleeve, and covers only a relatively narrow length portion of the sleeve. This results in a restricted area or length of the sleeve having the opening force applied thereto.
Various other attempts have been made to overcome this long existing problem but none have been completely satisfactory.